The Neuroscience Division of Children's Hospital works at the leading edge of developmental and genetic neuroscience, with particular strength in studies combining histochemistry and electron microscopy with computer-assisted reconstruction methods, to obtain three-dimensional views of neurons, their synaptic connections, chemistry, and developmental interrelationships. The pace of the research is severely constrained at present because of the progressively more limited reliability and stability of the JEOL transmission electron microscope that is at the heart of the instrumentation system. This grant application requests funds to replace the present electron microscope, after more than a decade of intensive use, with a new JEOL 100CX transmission electron microscope. The accessories required include: 1) 120KV accelerating voltage and minimum dose focusing to reduce speciman heating and subsequent destruction during exposure to the electron beam, 2) a goniometer with rotational holders for orienting ribbons of sections on sequential grids, 3) additional film canisters and cassettes to facilitate efficient photographing of serial sections from a single subject, or many different subjects at one photographic session, and 4) a free lens control system to allow continual as well as stepwise setting of the magnification. We expect the upgraded JEOL 100CX to serve several departmental investigators currently involved in biomedical research.